You can choose to use a subset of the buttons in the Buttons extension, or arrange some buttons in a collection. There are such examples on the DataTables website. We rewrite two simple examples in R below:

library(DT)
iris2 = head(iris, 20)
# only show the Copy and Print buttons
datatable(
  iris2,
  extensions = 'Buttons', options = list(
    dom = 'Bfrtip',
    buttons = c('copy', 'print')
  )
)
# put CSV, XLS, and PDF in a collection
datatable(
  iris2,
  extensions = 'Buttons', options = list(
    dom = 'Bfrtip',
    buttons = 
      list('copy', 'print', list(
        extend = 'collection',
        buttons = c('csv', 'excel', 'pdf'),
        text = 'Download'
      ))
    
  )
)